有限状态机—— FSM(finite-state machine)

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//有限状态机 finite-state machine

#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>

#define TTY1 "/dev/tty11"
#define TTY2 "/dev/tty12"
#define BUFSIZE 1024

enum
{
 STATE_R=1,
 STATE_W,
 STATE_Ex,
 STATE_T //finil state
};

struct fsa_st
{
 int state;
 int sfd,dfd;
 char buf[BUFSIZE];
 int len,pos;
 char *errstr;
};

static void fsa_driver(struct fsa_st *fsa)
{
 int ret;
  
 switch(fsa->state)
 {
  case STATE_R:
   fsa->len = read(fsa->sfd,fsa->buf,BUFSIZE);
   if(fsa->len == 0)
    fsa->state = STATE_T;
   else if(fsa->len < 0)
    {
     if(errno == EAGAIN)
      fsa->state = STATE_R;
     else
     {
      fsa->state = STATE_Ex;
      fsa->errstr = "read()";
     }
    }
    else
    {
     fsa->pos = 0;
     fsa->state = STATE_W;
    }
   break;

  case STATE_W:
   ret = write(fsa->dfd,fsa->buf+fsa->pos,fsa->len);
   if(ret < 0)
   {
    if(errno == EAGAIN)
     fsa->state = STATE_W;
    else
    {
     fsa->errstr = "write()";
     fsa->state = STATE_Ex;
    }
   
   } 
   else
   {
    fsa->pos += ret;
    fsa->len -= ret;
    if(fsa->len == 0)
     fsa->state = STATE_R;
    else
     fsa->state = STATE_W; 
   }
   break;

  case STATE_Ex:
   perror(fsa->errstr);
   fsa->state = STATE_T;
   break;

  case STATE_T:/*do nothing*/
   break;

  default:
   abort();
   break;
 }

}

static void relay(int fd1,int fd2)
{
 int fd1_save,fd2_save;
 struct fsa_st fsa12,fsa21;

 fd1_save = fcntl(fd1,F_GETFL);
 fcntl(fd1,F_SETFL,fd1_save|O_NONBLOCK);
 fd2_save = fcntl(fd2,F_GETFL);
    fcntl(fd2,F_SETFL,fd2_save|O_NONBLOCK);

 fsa12.state = STATE_R;
 fsa12.sfd = fd1;
 fsa12.dfd = fd2; 

 fsa21.state = STATE_R;
 fsa21.sfd = fd2;
 fsa21.dfd = fd1;

 while(fsa12.state != STATE_T || fsa21.state != STATE_T) //cann't is finil state
 {
  fsa_driver(&fsa12);
  fsa_driver(&fsa21);
 }
 // recover
 fcntl(fd1,F_SETFL,fd1_save);
 fcntl(fd2,F_SETFL,fd2_save);

}

int main()
{
 int fd1,fd2;
 
 fd1 = open(TTY1,O_RDWR);
 if(fd1 < 0)
 {
  perror("open()");
  exit(1);
 }
 write(fd1,"TTY1\n",5);

 fd2 = open(TTY2,O_RDWR|O_NONBLOCK);
    if(fd2 < 0)
    {
        perror("open()");
        exit(1);
    }
 write(fd2,"TTY2\n",5);

 relay(fd1,fd2);

 close(fd1);
 close(fd2);

 exit(0);
}

 

 

 

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